The present invention relates to non-metallic drive chains fitted with specialized attachments designed to perform load-inducing work on a cyclical basis. More specifically, the present invention discloses a stress relieving attachment for chains used in wastewater sedimentation tanks. These chains are equipped with elongate transverse flights which collect and convey settled sludge as well as floating waste to points of ultimate disposal within the tank.
Sludge collector mechanisms are used in the sedimentation tanks of wastewater and potable water treatment plants to scrape the settled sludge from the bottom of the tank and to skim the floating waste material from the surface of the wastewater. Typically, sludge collectors include transverse flights which are carried on a pair of drive chain strands on a circuit along the bottom of the tank as well as along the surface of the water in the tank to accomplish the scraping and skimming functions.
The end regions of collector flights are equipped with means to mount the flights on the drive chains. The drive chains are looped around collector chain sprockets which are mounted on cross shafts, with the sprockets located near the side walls of the tank to minimize shaft deflection.
In conventional applications, the collector flights are mounted to the drive chains by special attachment links, which are uniformly interspaced in each strand of drive chain. The attachment links essentially consist of a normal chain link provided with an upwardly projecting, paddle-faced integral member. This upwardly projecting member provides attachment points for threaded fasteners securing the flight to the chain.
The combined factors of cost, weight and corrosion have created a trend in the wastewater industry to greater use of plastics and other non-metallic materials. Consequently, the most recent developments in drive sprockets, chains, and even collector flights involve the implementation of non-metallic materials.
Recent attempts to design non-metallic flight attachment links have met with marginal success. Problems have arisen because elongate collector flights encounter significant stress loads originating in part from their long, unsupported mid-span area. This-mid span area is particularly susceptible to stress loads caused by accumulations of settled solids which must be pushed across the floor of the tank.
These stress loads are transmitted through the ends of the flight to the sidebars of the attachment links via the paddle-faced attachment point. The change in material plane and thickness at the junction of the paddle face and link sidebar results in an inherent stress concentration which renders the attachment link the weak link in the chain strand. The attachment link stress loading is compounded by reason that each attachment link progressing in the direction of chain travel will carry the load imposed by the trailing flights. It is the summation of the flight and chain loadings concentrated at the sidebar stress location that ultimately induces link failure. This is especially critical for chains installed in long settling basins.
Thus there is a definite need for a non-metallic drive chain flight attachment capable of withstanding the significant stress loads encountered by these components when used in wastewater treatment tanks.
It is the main object of the present invention to provide such an attachment.